(A) Field of the Invention
The present invention relates to a method for balancing the load of a wireless local area network, and more particularly, to a method for balancing the load of a wireless local area network with a plurality of access points, which conforms to IEEE 802.11 protocol.
(B) Description of the Related Art
In order to avoid jamming, it is better for a wireless local area network group in the same circumstance to use different channels separated by at least 25 MHz. For example, the available channel in the same circumstance are Channel 1, 6 and 11 for Northern America, Channel 1, 7 and 13 for European, and 1, 8 and 13 for Japan. Therefore, to install a plurality of access points (AP) in the same circumstance, it is better for the access points to use different channels, so as to avoid jamming.
FIG. 1 is a schematic diagram showing an association of a wireless local area network 10 with three access points wired on a local area network line 1 and several stations according to the prior art. According to the prior art, it is the stations and access points that decide whether to construct an association based only on the received signal strength indicator (RSSI). As shown in FIG. 1, the access points, 12, 22 and 32, are associated with the wireless local area network 10. Assume the access point 12 uses Channel 1, access point 22 uses the Channel 6 and access point 32 uses the Channel 11. Since the stations, 14, 16 and 18, are closer to the access point 12 and the RSSI from the access point 12 is stronger, the three stations are all associated with the access point 12. The stations, 34, 36 and 38, are all associated with the access point 32 since the stronger RSSI from the access point 32. When a station 40 tries to associate with the service set consisting of the access points, 12, 22 and 32, it will perform a scanning procedure to receive the beacon frame or the probe-response frame transmitted by the access points, 12, 22 or 32, and store the strengths of these packets. After the scanning procedure, the station 40 will select and associate with an access point with the strongest RSSI, i.e., the station 40 will associate with the access point 32. However, when the station 40 associates with the access point 32, the access point 32 has to provide transmission service to the station, 34, 36, 38 and 40, simultaneously. The service quality provided by the access point 32 is further decreased due to the overload. Contrary to the access point 32, the access point 22 is idle since it does not associate with any station.
According to the prior art, the station decides whether to associate with an access point only based on the RSSI. However, the prior art will lead many stations to associate with a minority of access points such as the access point 32. The transmission quality is decreased due to the overload of the access point, but some adjacent access points, such as the access point 22 are idle. In short, the prior art will lead to the unbalanced load between the access points with the same service set identifier.